Because of recent US-EPA rules, the traditional coliform test is no longer sufficient for water quality monitoring. One must now distinguish E. coli, the fecal indicator, from other coliforms that may grow as biofilms in water distribution systems. In recent years a number of tests for E. coli in drinking water have been developed. However, all these methods must be used in the cumbersome liquid fermentation format, either MPN tubes or in 100 ml presence-absence bottles. Because they are labor, material and time intensive, none of these are popular with test laboratories.
Membrane filtration is the overwhelming method of choice in water quality laboratories. However, a simple and economical membrane filter method for E. coli and total coliforms has never been developed. Even the method of Mates and Schaeffer (Membrane filtration differentiation of E. coli from coliforms in the examination of water, J. Appl. Bacteriol. 67, 343-346, 1989) requires two successive incubations on different media. This situation has forced the Millipore Corporation, the world's leader in membrane filter technology, to move away from filters and develop a liquid fermentation test for E. coli.
Public health and environmental monitoring would benefit enormously from a simple, inexpensive, one-step membrane-based test for enumerating E. coli and total coliforms.
Relevant Literature
Hensyl, et al. ed. Bergey's Manual of Determinative Bacteriology. 9th ed., particularly, pp. 202-289. Baltimore, Md.; Williams & Watkins 1994.